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190 lines
16 KiB
190 lines
16 KiB
From 5e9d5acbcd8ae45c4e736ac521fd2df5b1c62e25 Mon Sep 17 00:00:00 2001
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From: Ivan Kanakarakis <ivan.kanak@gmail.com>
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Date: Sat, 4 Jan 2020 00:39:47 +0200
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Subject: [PATCH] Fix XML Signature Wrapping (XSW) vulnerabilities
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PySAML2 did not check that the signature in a SAML document is enveloped and thus
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XML signature wrapping (XSW) was effective.
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The signature information and the node/object that is signed can be in different places
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and thus the signature verification will succeed, but the wrong data will be used. This
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specifically affects the verification of assertions that have been signed.
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This was assigned CVE-2020-5390
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Thanks to Alexey Sintsov and Yuri Goltsev from HERE Technologies to report this.
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+ + + + + + + +
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In more detail:
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libxml2 follows the xmldsig-core specification. The xmldsig specification is way too
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general. saml-core reuses the xmldsig specification, but constrains it to use of
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specific facilities. The implementation of the SAML specification is responsible to
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enforce those constraints. libxml2/xmlsec1 are not aware of those constraints and thus
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process the document based on the full/general xmldsig rules.
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What is happening is the following:
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- xmldsig-core allows the signature-information and the data that was signed to be in
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different places. This works by setting the URI attribute of the Reference element.
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The URI attribute contains an optional identifier of the object being signed. (see
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"4.4.3 The Reference Element" -- https://www.w3.org/TR/xmldsig-core1/#sec-Reference)
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This identifier is actually a pointer that can be defined in many different ways; from
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XPath expressions that need to be executed(!), to a full URL that should be fetched(!)
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in order to recalculate the signature.
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- saml-core section "5.4 XML Signature Profile" defines constrains on the xmldsig-core
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facilities. It explicitly dictates that enveloped signatures are the only signatures
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allowed. This mean that:
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* Assertion/RequestType/ResponseType elements must have an ID attribute
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* signatures must have a single Reference element
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* the Reference element must have a URI attribute
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* the URI attribute contains an anchor
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* the anchor points to the enclosing element's ID attribute
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xmlsec1 does the right thing - it follows the reference URI pointer and validates the
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assertion. But, the pointer points to an assertion in another part of the document; not
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the assertion in which the signature is embedded/enveloped. SAML processing thinks that
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the signature is fine (that's what xmlsec1 said), and gets the assertion data from the
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assertion that contains the signature - but that assertion was never validated. The
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issue is that pysaml2 does not enforce the constrains on the signature validation
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facilities of xmldsig-core, that the saml-core spec defines.
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The solution is simple; all we need is to make sure that assertions with signatures (1)
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contain one reference element that (2) has a URI attribute (3) that is an anchor that
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(4) points to the assertion in which the signature is embedded. If those conditions are
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met then we're good, otherwise we should fail the verification.
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Signed-off-by: Ivan Kanakarakis <ivan.kanak@gmail.com>
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---
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src/saml2/sigver.py | 49 ++++++++++++++++++++++++++++++++++++
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tests/saml2_response_xsw.xml | 6 +++++
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tests/test_xsw.py | 44 ++++++++++++++++++++++++++++++++
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3 files changed, 99 insertions(+)
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create mode 100644 tests/saml2_response_xsw.xml
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create mode 100644 tests/test_xsw.py
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diff --git a/src/saml2/sigver.py b/src/saml2/sigver.py
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index cbeca41f..c3d298a9 100644
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--- a/src/saml2/sigver.py
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+++ b/src/saml2/sigver.py
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@@ -1476,6 +1476,55 @@ def _check_signature(self, decoded_xml, item, node_name=NODE_NAME, origdoc=None,
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if not certs:
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raise MissingKey(_issuer)
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+ # saml-core section "5.4 XML Signature Profile" defines constrains on the
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+ # xmldsig-core facilities. It explicitly dictates that enveloped signatures
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+ # are the only signatures allowed. This mean that:
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+ # * Assertion/RequestType/ResponseType elements must have an ID attribute
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+ # * signatures must have a single Reference element
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+ # * the Reference element must have a URI attribute
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+ # * the URI attribute contains an anchor
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+ # * the anchor points to the enclosing element's ID attribute
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+ references = item.signature.signed_info.reference
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+ signatures_must_have_a_single_reference_element = len(references) == 1
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+ the_Reference_element_must_have_a_URI_attribute = (
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+ signatures_must_have_a_single_reference_element
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+ and hasattr(references[0], "uri")
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+ )
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+ the_URI_attribute_contains_an_anchor = (
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+ the_Reference_element_must_have_a_URI_attribute
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+ and references[0].uri.startswith("#")
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+ and len(references[0].uri) > 1
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+ )
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+ the_anchor_points_to_the_enclosing_element_ID_attribute = (
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+ the_URI_attribute_contains_an_anchor
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+ and references[0].uri == "#{id}".format(id=item.id)
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+ )
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+ validators = {
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+ "signatures must have a single reference element": (
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+ signatures_must_have_a_single_reference_element
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+ ),
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+ "the Reference element must have a URI attribute": (
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+ the_Reference_element_must_have_a_URI_attribute
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+ ),
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+ "the URI attribute contains an anchor": (
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+ the_URI_attribute_contains_an_anchor
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+ ),
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+ "the anchor points to the enclosing element ID attribute": (
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+ the_anchor_points_to_the_enclosing_element_ID_attribute
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+ ),
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+ }
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+ if not all(validators.values()):
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+ error_context = {
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+ "message": "Signature failed to meet constraints on xmldsig",
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+ "validators": validators,
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+ "item ID": item.id,
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+ "reference URI": item.signature.signed_info.reference[0].uri,
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+ "issuer": _issuer,
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+ "node name": node_name,
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+ "xml document": decoded_xml,
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+ }
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+ raise SignatureError(error_context)
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+
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verified = False
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last_pem_file = None
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diff --git a/tests/saml2_response_xsw.xml b/tests/saml2_response_xsw.xml
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new file mode 100644
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index 00000000..3671eb48
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--- /dev/null
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+++ b/tests/saml2_response_xsw.xml
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@@ -0,0 +1,6 @@
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+<?xml version="1.0" encoding="UTF-8"?>
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+<ns0:Response xmlns:ns0="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:ns1="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:ns2="http://www.w3.org/2000/09/xmldsig#" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Destination="http://lingon.catalogix.se:8087/" ID="id-vqOQ72JCppXaBWnBE" InResponseTo="id12" IssueInstant="2019-12-20T12:15:16Z" Version="2.0"><ns1:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">urn:mace:example.com:saml:roland:idp</ns1:Issuer><ns0:Status><ns0:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/></ns0:Status><ns1:Assertion ID="id-SPOOFED_ASSERTION" IssueInstant="2019-12-20T12:15:16Z" Version="2.0"><ns1:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">urn:mace:example.com:saml:roland:idp</ns1:Issuer><ns2:Signature Id="Signature2"><ns2:SignedInfo><ns2:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/><ns2:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/><ns2:Reference URI="#id-Aa9IWfDxJVIX6GQye"><ns2:Transforms><ns2:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/><ns2:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/></ns2:Transforms><ns2:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/><ns2:DigestValue>EWBvQUlrwQbtrAjuUXkSBAVsZ50=</ns2:DigestValue></ns2:Reference></ns2:SignedInfo><ns2:SignatureValue>m4zRgTWleMcx1dFboeiYlbiDigHWAVhHVa+GLN++ELNMFDutuzBxc3tu6okyaNQGW3leu32wzbfdpb5+3RlpGoKj2wPX570/EMJj4uw91XfXsZfpNP+5GlgNT8w/elDmBXhG/KwmSO477Imk0szKovTBMVHmo3QOd+ba//dVsJE=</ns2:SignatureValue><ns2:KeyInfo><ns2:X509Data><ns2:X509Certificate>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</ns2:X509Certificate></ns2:X509Data></ns2:KeyInfo></ns2:Signature><ns1:Subject><ns1:NameID Format="urn:oasis:names:tc:SAML:2.0:nameid-format:transient" NameQualifier="" SPNameQualifier="id12">ANOTHER_ID</ns1:NameID><ns1:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer"><ns1:SubjectConfirmationData InResponseTo="id12" NotOnOrAfter="2019-12-20T12:20:16Z" Recipient="http://lingon.catalogix.se:8087/"/></ns1:SubjectConfirmation></ns1:Subject><ns1:Conditions NotBefore="2019-12-20T12:15:16Z" NotOnOrAfter="2019-12-20T12:20:16Z"><ns1:AudienceRestriction><ns1:Audience>urn:mace:example.com:saml:roland:sp</ns1:Audience></ns1:AudienceRestriction></ns1:Conditions><ns1:AuthnStatement AuthnInstant="2019-12-20T12:15:16Z" SessionIndex="id-eEhNCc5BSiesVOl8B"><ns1:AuthnContext><ns1:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:InternetProtocolPassword</ns1:AuthnContextClassRef><ns1:AuthenticatingAuthority>http://www.example.com/login</ns1:AuthenticatingAuthority></ns1:AuthnContext></ns1:AuthnStatement><ns1:AttributeStatement><ns1:Attribute FriendlyName="eduPersonAffiliation" Name="urn:oid:1.3.6.1.4.1.5923.1.1.1.1" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">staff</ns1:AttributeValue><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">ADMIN</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="mail" Name="urn:oid:0.9.2342.19200300.100.1.3" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">HACKER@gmail.com</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="givenName" Name="urn:oid:2.5.4.42" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">Derek</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="surName" Name="urn:oid:2.5.4.4" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">Jeter</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="title" Name="urn:oid:2.5.4.12" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">shortstop</ns1:AttributeValue></ns1:Attribute></ns1:AttributeStatement></ns1:Assertion>
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+<XSW_ATTACK>
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+<ns1:Assertion ID="id-Aa9IWfDxJVIX6GQye" IssueInstant="2019-12-20T12:15:16Z" Version="2.0"><ns1:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">urn:mace:example.com:saml:roland:idp</ns1:Issuer><ns1:Subject><ns1:NameID Format="urn:oasis:names:tc:SAML:2.0:nameid-format:transient" NameQualifier="" SPNameQualifier="id12">ac5b22bb8eac4a26ed07a55432a0fe0da243f6e911aa614cff402c44d7cdec36</ns1:NameID><ns1:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer"><ns1:SubjectConfirmationData InResponseTo="id12" NotOnOrAfter="2019-12-20T12:20:16Z" Recipient="http://lingon.catalogix.se:8087/"/></ns1:SubjectConfirmation></ns1:Subject><ns1:Conditions NotBefore="2019-12-20T12:15:16Z" NotOnOrAfter="2019-12-20T12:20:16Z"><ns1:AudienceRestriction><ns1:Audience>urn:mace:example.com:saml:roland:sp</ns1:Audience></ns1:AudienceRestriction></ns1:Conditions><ns1:AuthnStatement AuthnInstant="2019-12-20T12:15:16Z" SessionIndex="id-eEhNCc5BSiesVOl8B"><ns1:AuthnContext><ns1:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:InternetProtocolPassword</ns1:AuthnContextClassRef><ns1:AuthenticatingAuthority>http://www.example.com/login</ns1:AuthenticatingAuthority></ns1:AuthnContext></ns1:AuthnStatement><ns1:AttributeStatement><ns1:Attribute FriendlyName="eduPersonAffiliation" Name="urn:oid:1.3.6.1.4.1.5923.1.1.1.1" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">staff</ns1:AttributeValue><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">member</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="mail" Name="urn:oid:0.9.2342.19200300.100.1.3" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">foo@gmail.com</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="givenName" Name="urn:oid:2.5.4.42" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">Derek</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="surName" Name="urn:oid:2.5.4.4" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">Jeter</ns1:AttributeValue></ns1:Attribute><ns1:Attribute FriendlyName="title" Name="urn:oid:2.5.4.12" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"><ns1:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">shortstop</ns1:AttributeValue></ns1:Attribute></ns1:AttributeStatement></ns1:Assertion>
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+</XSW_ATTACK>
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+</ns0:Response>
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diff --git a/tests/test_xsw.py b/tests/test_xsw.py
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new file mode 100644
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index 00000000..9978c4d3
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--- /dev/null
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+++ b/tests/test_xsw.py
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@@ -0,0 +1,44 @@
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+from datetime import datetime
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+from unittest.mock import Mock
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+from unittest.mock import patch
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+
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+from saml2.config import config_factory
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+from saml2.response import authn_response
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+from saml2.sigver import SignatureError
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+
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+from dateutil import parser
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+
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+from pytest import raises
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+
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+from pathutils import dotname
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+from pathutils import full_path
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+
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+
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+XML_RESPONSE_XSW = full_path("saml2_response_xsw.xml")
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+
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+
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+class TestAuthnResponse:
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+ def setup_class(self):
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+ self.conf = config_factory("sp", dotname("server_conf"))
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+ self.ar = authn_response(self.conf, "http://lingon.catalogix.se:8087/")
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+
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+ @patch('saml2.response.validate_on_or_after', return_value=True)
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+ def test_verify_signed_xsw(self, mock_validate_on_or_after):
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+ self.ar.issue_instant_ok = Mock(return_value=True)
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+
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+ with open(XML_RESPONSE_XSW) as fp:
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+ xml_response = fp.read()
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+
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+ self.ar.outstanding_queries = {"id12": "http://localhost:8088/sso"}
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+ self.ar.timeslack = 10000
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+ self.ar.loads(xml_response, decode=False)
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+
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+ assert self.ar.came_from == 'http://localhost:8088/sso'
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+ assert self.ar.session_id() == "id12"
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+ assert self.ar.issuer() == 'urn:mace:example.com:saml:roland:idp'
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+
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+ with raises(SignatureError):
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+ self.ar.verify()
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+
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+ assert self.ar.ava is None
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+ assert self.ar.name_id is None
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